In sports training, an athlete's training process is normally directed by a coach. The coach typically designs training sessions and monitors the athlete's performance. In this traditional framework, the assessment of an athlete's performance largely depends on the coach's experience, judgment, and patience. It is often difficult for the athlete to receive instant feedback from the coach. In addition, the feedback may not be based on objective measures. In physical therapy especially rehabilitation treatment, a physician often assesses a patient's condition based on overall physical appearance. Subtle imperfections, such as slight imbalance between injured and non-injured legs, are difficult to capture. Therefore, it is desirable to develop systems and methods for providing instant feedback and objective assessment of the effectiveness of physical training.